Collated screwstrips are known in which the screws are connected to each other by a retaining strip of plastic material. Such strips are taught, for example, by U.S. Pat. No. 4,167,229 issued Sep. 11, 1979 and its related Canadian Patents 1,040,600 and 1,054,982 as well as U.S. Pat. No. 4,930,630, the disclosures of which are incorporated herein by reference. Screws carried in such screwstrips are adapted to be successively incrementally advanced to a position in alignment with and to be engaged by a bit of a reciprocating, rotating power screwdriver and screwed into a workpiece. In the course of the bit engaging the screws and driving it into a workpiece. In the course of the bit engaging the screw and driving it into a workpiece, the screw becomes detached from the plastic strip leaving the strip as a continuous length.
In the use of such collated screwstrips in screwdrivers, the strip serves a function of assisting in guiding the screw into a workpiece and, to accomplish this, the strip is retained against movement towards the workpiece. In the screwstrip, each screw to be driven has its threaded shaft threadably engaged in a threaded sleeve of the strip such that on the screwdriver engaging and rotating each successive screw, the screw turns within the sleeve which acts to guide the screw as it moves forwardly into threaded engagement into the workpiece. Preferably, only after the tip of the screw becomes engaged in the workpiece, does the head of the screw come into contact with the sleeves. Further, forward movement of the screw into the workpiece then draws the head downwardly to engage the sleeve and to rupture the sleeve by reason of the forward movement of the head with the strip retained against movement towards the workpiece. The sleeve preferably is configured to have fragile strips which break on the head passing through the sleeve such that the strip remains intact as a continuous length. Since the strip is a continuous length, on advancing the screwstrip with each successive screw to be driven, it necessarily results that portion of the strip from which each screw has been driven are also advanced to exit from the power screwdriver.
Known power screwdrivers for driving such collated screwstrips include U.S. Pat. No. 4,146,871 to Mueller et al, issued Mar. 27, 1976, and U.S. Pat. No. 5,186,085 to Monaceli, issued Feb. 16, 1993, the disclosure of which are incorporated herein by reference. Such known power screwdrivers include a rotatable and reciprocally moving screwdriver shaft which is turned in rotation by an electric motor. A screwdriving bit forms a forwardmost portion of the shaft for engaging the head of each successive screw as each screw is moved into a driving position, axially aligned under the screwdriver shaft.
An important aspect of such power screwdriver is the manner and accuracy with which the screws are advanced and positioned so as to be properly aligned axially under the screwdriver shaft for successful initial and continued engagement between the bit and the screwdriver head in driving a screw fully down into a workpiece. In the device of Mueller et al, a guide channel is provided through which the screwstrip is advanced. The guide channel is sized to receive screws of specific head size and minimum length. The guide channel is formed as an integral part of a sliding body which also carries other components of a screw advance mechanism including a feed pawl to engage the screwstrip and thereby advance successive screws in the screwstrip. The screws are successively advanced into position in alignment with the screwdriver shaft with the heads of the screws being urged into abutment with a stop which is to locate the screw head. The stop typically defines a radial extent of a boreway through which the shaft and screw head axially move as the screw is driven.
The shaft is axially movable in the boreway in a reciprocal manner to engage the screw and drive it into a workpiece. After each screw is driven the shaft retracts and a subsequent screw carried on the screwstrip is advanced sideways into the boreway, engaging the stop so as to be aligned under the shaft.
A disadvantage with screwdrivers such as taught by Mueller et al and others is that the screwdrivers are not adapted to drive different sized screwstrips or screws. Known screw drivers have a guide channel with is sized to receive only screws of certain dimensions. Similarly, the screw advance mechanism is adapted only to advance screws by contacting screws and/or the strips at certain places determined by the size of the screws and configuration of the screwstrips. As well, the screw advance mechanism is adapted only to advance the screwstrip a certain maximum stroke determined by one pre-selected spacing of the screws on the strip. Any stop provided to located screw heads if adjustable, is typically only adjustable to accommodate screws of slightly varying head sizes. The construction of most known screwdrivers and particularly of their screw guide channels, screw advance mechanisms and screw locating stops has the disadvantage of not permitting one screwdriver to practically be adjusted to drive screwstrips and/or screws of different sizes. Another disadvantage is that most screwdrivers cannot drive the last screw in a strip. Most screwdrivers suffer the disadvantage of requiring a number of moving parts to located each screw to be driven.